1. Field of the Invention
The present invention relates to devices for operation of switching elements in an electrical circuit, and more particularly, the present invention relates to remote controlled rocket devices for providing propelling forces to provide high speed operation of switching elements in an electrical circuit where either attended or unattended operation is required.
2. Description of the Prior Art
In recent years electric utilities have experienced difficulty in providing adequate protection for operating personnel when closing switching devices with conventional operating tools to energize overhead distribution transformers. A combination of new practice in transformer design, traditional fusing practice, higher fault current levels, and higher distribution voltages has led to explosive failures of transformer tanks resulting from internal arcing faults. Such arcing faults within the transformer's insulating oil generate an internal pressure build-up within the tank due to "let-through" current of the protective device, sometimes resulting in tank rupture or transformer cover being disruptively blown off the tank. It is evident, therefore, that, as an alternative to installing new circuit protective devices to restrain the level of the "let-through"current, the safety of operating personnel would be enhanced by the use of a tool which can be installed on most existing conventional switching devices (such as fuse cutout and power fuses as typically utilized for protection of overhead transformer installations) and which facilitates the closing of said switching devices from remote locations.
One type of prior art device which is utilized to achieve a similar safety factor is described in U.S. Pat. No. 3,810,060. This device is a portable tool consisting of a conventional switching element (fuse cutout) especially fitted with lever and lanyard rigged to the ground through a pulley mounted near the base of the transformer pole to facilitate an approximate 90.degree. translation in the force exerted on the lanyard, thereby allowing personnel located at ground level and at considerable distance away from the base of the pole to close the switching element by pulling the lanyard. Following successful energization of the transformer, the permanently mounted conventional transformer protective device must be closed electrically in parallel with the portable tool in the conventional manner using a conventional switch operating tool. The portable tool and its rigging must then be manually removed.
Another type of prior art device consists of the use of a current limiting fuse as a portable tool for closing the circuit. Following successful energization of the transformer through the current-limiting fuse (specifically selected to preclude a disruptive transformer failure), the permanently mounted conventional transformer protective device is electrically closed in parallel. Finally, as in the above example, the portable tool must be manually removed from the overhead line.
Accordingly, it would be a beneficial advance to the art to provide an inexpensive, convenient and expendable device for manually closing the permanently installed conventional transformer switching element such as fuse cutout or power fuse from a remote location without the need to spend time and effort to recover the tool and related equipment.
Also, for many years electric utilities have utilized high-speed grounding switches to convert relay-detected low-level, secondary-side transformer faults into heavy primary-side ground fault capable of being detected and cleared by the source circuit breakers. Following such clearing of both faults, an automatically controlled disconnect switch isolates both the faulted transformer and the closed high-speed grounding switch, thereby allowing the source circuit breaker to reclose in order to restore service to the unaffected loads fed by the same source. Additionally, three-pole, high-speed grounding switches are utilized to convert a relay-detected, low-level transformer fault into a heavy ground fault in order to force simultaneous operation of, and effect isolation by, all three fuses feeding a three-phase transformer.
In order to minimize outage time for unaffected loads as well as to minimize fault damage to the affected transformer, high speed is an obvious requirement. Presently, high-speed grounding switches close by means of a solenoid releasing the energy of a torsional spring to propel the switch blade. Accordingly, it would be a beneficial advance to the art to provide a less expensive, yet higher speed grounding switch powered by an electrically ignited rocket engine (or the cluster of engines as may be required to attain the desired speed) in lieu of a heavy-duty spring and solenoid-release mechanism.